Transmission regulation



March 28, 1939. .1. 6. WILSON 2,151,821

TRANSMISSION REGULATION Filed May 15, 1937 INVENTOR By /.G. W/L SON A TTORNE Y 1 mission control. In accordance with the prior scribed- Subsequontly- Patented Mar. 28, 1939 v v I UNITED STATES PATENT OFFICE TRANSMISSION REGULATION Ira G. Wilson, Brooklyn, N. Y., assignor to Bell 7 Telephone Laboratories, Incorporated; New

York, N. Y., a corporation of New York Application May 15, 1937. Serial No.-142,831

7 claims. (01. 178-44 W This invention relates to control circuits for renders the elementsmore accessible and more adjusting'the gain on signal transmission lines easily mounted. Means are provided for autoand particularly to a circuit for automatically admatically maintaining the temperature of the justing the gain at repeater stations associated elements at a constant value regardless of the with transmission lines. rate of radiation; the rate of radiation will vary It is well known that in certain types of tran of course in accordance with variations in the mission lines, such as long telephone lines, ambient t p t a t e pe t changes in attenuation of the line occur from A full understandingof the a r e t 0 ntime to time due to temperature changes. These p t d y t invention as w as pp 1i) temperature changes may be due to climatic tion of the various valuable features thereof may 10 ditions, or in certain cases, to the heating efiect be gained from Consideration of the following of the signaling curr nts, I rd t compensate tailed description in connection with the annexed for the effect of such attenuation changes it is drawing in Whioh'the Single fi u e iS a Schematic usual to provide means for adjusting the gain of diagram of a circuit em odying the gain regulatthe various repeaters provided on the line autoing arrangement o templated by the invention. 15 ti uy, Referring now to the drawing, line H which is An object of the invention is to adjust the gain Shown s assumed to be e o a number of simof a repeater associated with a transmission line 1131 lines grouped together and p e ably enauto ati all i h manner as t compensate closed by a lead sheath, forming a cable of standfor changes in attenuation of the line due to temand construction; Each line is ed at i perature changes. tervals with a repeater, repeater l2 being shown A more pecific obje t of the invention is to associated with line H. Inthe case of lines transadjust the gain of a repeater automatically in muting Voice currents the repeaters may be such a manner as to compensate f changes in spaced at intervals of about fifty miles while in the ambient temperature at the repeater station. I W case of lines transmitting high frequency 2.

In accordance with one embodiment of the in- Her Waves the repeaters may be ped much v ti repeater gain is Controlled by use of closer togethenior example, at intervals of about thermo-sensitive elements, i. e., elements the reten miles- Repeater is preferably of the S ebisi t of which changes as their temperature lized feedbacktype having a feedback path l3 exchanges. The temperature of these elements is tending from its output book to its input controlled in accordance with change of line atfeeding back Waves n a manner effective to t ati duce the gain of the repeater thereby increasing In accordance ith featur f t invention its stability and improving its linearity. For a the temperature of the thermo-sensitive elements l disclosure of the ement and operais a t ti n varied t compensate the tion of amplifiers of the feedback type reference 3 effects thereon of changes in the ambient may be made to Patent 2,102,671 issued December peraturs 21, 1937 to H. S. Black, Wave translation sys- The use of thermo-sensitive elements in gain temp V control circuits has been proposed heretofore, While applicant's invention is being disclosed in 40 such arrangements being described for exampl connection with an amplifier of the feedback 0 in Patent 2,098,968 issued November 16, 1937 to type, it will be understood that t e types of C. O. Mallinckrodt, Transmission regulation, amplifiers may be used, Suitable Provisions being and Patent,2,l16,600 issued May 10,1938 to J. R. included for changing the i thereof under Fisher and C. O. Mallinckrodt, Electrical transcontrol of regulating pp tus to be do arrangements t h b t usual practice to Line I6 is enclosed within the same sheath as enclose the thermo-sensitive elements in a heatline H and the other lines C pr ing the cable.

, ing chamber whereby radiation from the elements Line extends the length of one epeater seccould be controlled within certain limits. In t i looped at h r end, and forms what is accordance with the arrangement invented by commonly known as the Pilot Wi e. Line [6, applicant, however, no heat chambers are 'utiw ch is p ovided for purposes of regulation is lized, the elements being exposed directly to the S ject, of course, to the same variations in tematmosphere. This practice results in important perature'as the other l nes, such as line H, of the advantages from an economic standpoint and cable. s is The regulating mechanism, which includes bridge H, is controlled largely by line l6. Bridge |1 comprises four resistance arms, one arm comprising fixed resistance |8, a second arm comprising fixed resistance 2| in series with the resistance of line I6, which varies in accordance with temperature changes, a third arm comprising fixed resistance 22 in series with resistance 23 which is varied by operation of the bridge galvanometer, and the fourth arm comprising fixed resistance 26 in series with variable resistance 21, variable resistance 28 being connected in parallel to resistance 21. Variable resistance 21 is a thermosensitive element having a negative temperature coeflicient of resistance, for example a boron element.

Automatic galvanometer 4| which is associated with bridge l1, may be, for example, of the type disclosed in Ulrich Patent 1,647,383 issued November 1, 1927. The galvanometer assembly includes a source of mechanical power for rotating shaft 42 through an angle proportional to the angle of deflection of the galvanometer resulting from an unbalanced condition of the bridge. Contact arms 43 and 46 are carried by shaft 42 and determine respectively by their positions the portions of resistances 23 and 41 which are effectively connected in the circuit.

Battery 48 provides the necessary current for bridge I 1.

Thermo-sensitive resistance 56, which should be of the same material as element 21, is provided with heater 58, the two being mounted in close association or, if preferable, being actually combined in a unitary structure. Similarly, thermo-sensitive resistances 1| and 12, likewise of the same material as element 21, are provided with respective heaters 11 and 18. Resistance 56 is connected to control the gain of repeater l2 while resistances 1| and 12 may be similarly connected to control other repeaters not shown.

Heaters 58, 11 and 18 which are associated respectively with thermo-sensitive elements 56, 1| and 12 as well as heater 9| which is associated with thermo-sensitive resistance 21 of bridge H are energized over a common heater line 92. Battery 93 supplies current to line 92 under control of variable resistance 41. In practice the heater current is so regulated that the temperature of the thermo-sensitive elements is maintained at a point substantially higher than the ambient temperature of the repeater station.

In order to further described the invention, let us assume that the temperature of the cable increases thereby increasing the transmission loss in line I and the other lines included in the cable. There will be, of course, a corresponding increase in the temperature of pilot line IS, the resulting increase of resistance thereof unbalancing bridge I1. .Movement of automatic galvanometer 4|, resulting from the unbalanced condition of the bridge rotates shaft 42 and contact arms 43 and 46 carried thereby, through an angle proportional to the unbalance of the bridge.

Readjustment of resistance 23 by movement of contact arm 43 is effective to rebalance the bridge while readjustment of resistance 41 by movement of contact arm 46 is effective to cause an increase of the current fiow in heater line 92 thereby resulting in an increase of the temperature of heaters 58, 11, 18 and 9|.

In view of the negative temperature coeflicient of resistance of element 56 (preferably boron) the resistance thereof will be decreased by the rise in temperature of heater 58, thereby causing the element to shunt a greater portion of the current in the feedback circuit of amplifier l2. This reduces the amount of feedback and since the feedback is a gain reducing feedback this results in raising the amplification of repeater |2 thereby compensating for the increase in the transmission loss in line I.

Elements 1| and 12 act in a similar manner to increase the gain of the amplifiers with which they are associated.

While the decrease in resistance of element 21, resulting from the rise in temperature of heater 9|, unbalances bridge I 1 slightly, resulting movement of galvanometer 4| brings the bridge back into a stable condition.

Let us assume now that there is no further change in the temperature of the cable for the present but that there is a change in the ambient temperature of the repeater station, for example, a considerable decrease of temperature. This will result, of course, in a more or less rapid radiation of heat from element 56 to the cool air surrounding it thereby tending to increase its resistance. Such an increase if persistent would,

of course, be undesirable as it would cause a decrease in the gain of amplifier 2. However, in accordance with applicant's invention this undesirable change is prevented due to the fact that provisions are made for bringing about an unbalanced condition of bridge I1 and readjustment of the heater current to compensate for the ambient temperature variation.

It will be evident that the temperature of element 21 will decrease at a rate corresponding to that at which the temperature of element 56 decreases, thereby resulting in an increase of the resistance of element 21 corresponding to the increase of resistance of element 56. The change in resistance of element 21, however, unbalances bridge |1, thereby causing movement of automatic galvanometer 4|. The resulting readjustment of resistance 23 brings the bridge back into balanced condition while the readjustment of resistance 41 causes an increase of current flow in heater line 92 sufiicient to increase the temperature of elements 56 and 21 a sufiicient amount to compensate for the change in ambient temperature. The temperature of element 56 is maintained at a constant value, therefore, notwithstanding the decrease in the ambient temperature of the repeater station.

The resistance of elements 1| and 12 is, of course, maintained at a constant value also in view of the fact that the associated heaters are energized over the same path as heater 58.

It will be understood that the arrangement functions in a similar manner to compensate for increases in the ambient temperature, the bridge being unbalanced in such a case to bring about a decrease of the heater current. The fact that an element is included in an arm of the bridge which is of similar material to the compensating elements included in the feedback path of the amplifier and which is heated from the same circuit and subject to the same ambient temperature, results in an arrangement which maintains the temperature of the gain-compensating elements constant regardless of changes in ambient temperature.

While the use of boron elements as the temperature-responsive resistances has been described, it will be understood that other substances having like characteristics may be used instead of the boron. By way of example, silver sulphide elements may be substituted for the boron elements. In such event, however, it may be found desirable to utilize an alternating current source in the bridge instead of the direct current source described (battery 48) in order to prevent deterioration of the silver sulphide due to the efiects of direct current.

While a certain specific embodiment of the invention has been selected for detailed description the invention is not, of course, limited in its application to the embodiment described. For example, the regulating arrangement described may be utilized in connection with networks rather than repeaters and may be controlled by means other than, a pilot Wire regulated bridge. In short, the embodiments described should be taken as illustrative and not as restrictive.

What is claimed is:

1. In a regulating system for transmission lines including repeaters, a Wheatstone bridge, means for controlling the balance of said bridge in accordance with line attenuation, a thermo-sensitive element included in a resistance arm of said bridge, a heater for said thermo-sensitive element, a second thermo-sensitive element adapted to control the gain of a repeater, a heater for said second thermo-sensitive element, said elements being directly exposed to the free atmosphere, a single source of heating current for both of said heaters, and means controlled by an unbalanced condition of said bridge for controlling the supply of current from said source to said heaters.

2. In a regulating system for transmission lines including repeaters, a Wheatsone bridge, a circuit for controlling the balance of said bridge in accordance with line attenuation, a thermo-sensitive element included in a resistance arm of said bridge, a heater for said element, a second thermo-sensitive element adapted to control the gain of a repeater, a heater for said second element, both of said elements being directly exposed to the free atmosphere, a source of heating current, a heating circuit common to said source and to said heaters, and means controlled by an unbalanced condition of said bridge for controlling the current in said heating circuit.

3. In a regulating system for transmission lines including repeaters, a Wheatstone bridge, a circuit for controlling the balance of said bridge in accordance with line attenuation, a thermo-sensitive element included in one of the resistance arms of said bridge, a heater for said element, a second thermo-sensitive element adapted to" control the gain of a repeater, a heater for said second element, said thermo-sensitive elements being so located with respect to each other that they are incapable of being heated by radiation from a common heater element, a single source of heating current for said heaters, and means controlled by an unbalanced condition of said bridge for controlling the supply of heating current from said source to said heaters.

4. In a regulating system for transmission lines including repeaters, a repeater station, a Wheatstone bridge, means included in one resistance arm of said bridge for controlling the balance of said bridge in accordance with line temperature, means included in another resistance arm of said bridge for controlling the balance thereof in accordance with the ambient temperature of the repeater station, a heater for said last-mentioned means, a thermo-sensitive element at the repeater station adapted to control the gain of a repeater, said thermo-sensitive element being directly exposed to the atmosphere, a heater for said thermo-sensitive element, a source of heating current, and means controlled by an unbalanced condition of said bridge for controlling the supply of current from said source to said heaters.

5. In a regulating system for transmission lines, a repeater station, repeaters at said station, a Wheatstone bridge, a circuit for controlling the balance of said bridge in accordance with line attenuation, a thermo-sensitive resistor in one resistance arm of said bridge, a heater for said resistor, a second thermo-sensitive resistor adapted to control the gain of a repeater, a heater for said second resistor, said resistors being located at separate points in said station, a source of heating current, means for supplying current from said source to said heaters, and means controlled by changes in ambient temperature at said repeater station for controlling the magnitude of the heating current supplied to said heaters from said source.

6. In a regulating system for transmission lines including repeaters, said system comprising a pilot conductor and a Wheatstone bridge controlled thereby, a thermo-sensitive element adapted to control the gain of a repeater, a second thermosensitive element, said second thermo-sensitive element being connected to said bridge and effective to unbalance said bridge upon a change in ambient temperature, both of said thermo-sensitive elements being directly exposed to the free atmosphere, a heater for each of said elements, a source of heating current, and means controlled by an unbalanced condition of said bridge for controlling the supply of current from said source to said heaters.

'7. In a transmission regulating system, a thermo-sensitive transmission regulating element, means including a local source of heating current for controlling the temperature of said element, means for compensating for the effect on said element of variations in atmospheric temperature, said last-mentioned means comprising a second thermo-sensitive element effective to modify the operation of said first-mentioned means, both of said thermo-sensitive elements being exposed directly to the free atmosphere.

IRA G. WILSON. 

